Impulse and impact noise are important factors in the production of hearing loss in industrial and military settings. This project continues to have three objectives: (1) establish the relation between the acoustic parameters of an impulse i.e., intensity, repetition rate, rise-time, spectrum, number of impulses and the resultant hearing loss; (2) document the sequence of changes associated with exposure to impulse/impact noise using electrophysiological and anatomical techniques; (3) document the audiological changes associated with exposure to impulse/impact noise with an electrophysiological test battery i.e., quite thresholds, tuning curves and forward masking functions. All these experiments are to be conducted on chinchillas using experimental procedures that are well developed. The significance of this project is that it will be possible to establish future scientifically based noise standards using the results of our systematic parametric studies of impulse and impact noise. In particular, the results will address the appropriateness of the Equal Energy Hypothesis for impulse/impact noise.